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By A. W. Meyer, M. D.
 
By A. W. Meyer, M. D.

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References - Essays on the History of Embryology  

Meyer AW. 1932 - Essays on the History of Embryology: Part I | Part II | Part III | Part IV | Part V | Part VI | Part VII | Part VIII | Part IX | Part X | Part XI | Arthur Meyer | Historic Embryology Papers

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Arthur William Meyer (1873 – 1966)
Arthur William Meyer (1873 – 1966)

Essays on the History of Embryology VII

By A. W. Meyer, M. D.

Stanford University

This is the seventh paper of a series of essays on this subject. Previous papers were printed in this journal as follows: Part I, in December California and Western Medicine, page 447: Part II, in January number, page 40; Part III, in February number, page 105: Part IV, in March number, page 176; Part V, in April number, page 241; Part VI, in May number. page 341.


Author's Note.— Through an oversight John Hunter instead of William was credited with the authorship of the Anatomia Uteri Humani Gravida in the May installment of my essays. This is especially embarrassing because of John’s remark about stuffing him with Latin and Greek. My sympathy has always been with him, and it seems highly probable to me that he really made the discovery regarding the utero-placental circulation. which is announced in the royal folio by William. In my enlarged manuscript I attempt to accord John recognition so long withheld him, for among other things embryological, John made an unequivocal statement of the law of recapitulation, usually attributed to Fritz Müller about half a century latter.


IT is illogical as well as impossible to isolate the story of experimental embryology, for it is inextricably interwoven with the rest of it. My reason for giving separate consideration to experimental investigation is not because I regard such as more reliable or important than observation, but because a single experiment sometimes greatly and unexpectedly narrowed the horizon of futile speculation, and thus ended long-continued controversy or gave it new direction.


Even though the statement attributed to Pliny that the best results in‘ the hatching of hen eggs are obtained after the eggs are ten days old is incorrect, it suggests that experiments upon these things had probably been made by that time. The same thing applies to the report of Diodorus (Siculus) that the Egyptians in the first century before Christ were using incubators, warmed by a fire,‘ for the hatching of hen eggs. Since this could not well be done without observing the conditions concerned in incubation, it is more than likely that experiments in embryology were made in ancient Egypt as well, so that the history of experimental embryology probably extends farther back than that of morphologic embryology. Whether he wished it or not, even primitive man was often compelled by circumstances to undertake experiments. The method of trial and error is an old thing in the ascent of man. The evolution of tools and weapons alone illustrates this.

Word “Experiment” as Here Used

In considering the early history of experimentation, I shall use the word “experiment” in a very general sense. I shall assume that anyone who put eggs under a hen or semen on an object carrier, however primitive, for the purpose of examining them from time to time was doing an experiment. I should take the same attitude regarding him who took reptilian eggs that he found in the sands of the seashore, in order to observe their incubation. Such a use of the word “experiment” also is in accord with that in the days of Redi and Spallanzani.


There undoubtedly were many who did experiments regarding whom the records were lost. Those who are familiar with Redi’s work will recall that toward the end of his long letter to Carlo Dati, he wrote: “I tried a great many other experiments, and made many observations, but owing to carelessness, some pages on which I had inscribed them were mislaid.” Réaumur, too, undoubtedly did many experiments of which I unfortunately have been unable to learn. We know that Harvey, Redi, Spallanzani, Réaumur, Malpighi, and many others of their day experimented in many fields of physics or nature, even if not predominantly along the line of embryology or what was then called generation.


Reference has already been made to the statement of a Hippocratic writer that if one desires to learn about the development of the chick one must put twenty—one eggs under a hen and remove one daily for examination. It may also be recalled that Aristotle suggested a flotation test for determining the fertility of semen. His idea was that if semen floated it had lost its fertilizing power and hence was sterile. The assertion of Aristotle that heat solidifies semen and that cold thins it also suggests that he may have experimented further in this connection, although Aristotle probably used the words “heat” and “cold” in a different sense. Such experiments as these well may have been sporadic, but the fact that they were undertaken, or even considered, suggests that many others may have been tried but were regarded as not being significant. The men of the past surely were not wholly without inclination to experimentation and they did not lack stimuli towards it.


Fig. 1. — One of Leeuwenhoek‘s microscopes, actual size. (I) and (II), front and back respectively. (c) Lens. (g) adjusting screw, (h) stage, (i) rotating object carrier, (k) handle of same, (1) adjusting screw.


Views of Paracelsus

I know of nothing more unique in the whole history of embryology than the method for the alleged production of human beings given by Paracelsus. When referring to it in his very interesting treatise on the artificial changling, John Bulwer wrote:

"Paracelsus boasts that he had received this secret of secrets from God; affirming, that if the sperm of a man do putrifie in a sealed Gourd, to the highest putrification of horse-dung, forty daies, or so long untill it begin to live, and to move, and be stirred, which is easie to be seen, after that, it will be in some time like unto a man, yet pellucid and without a body: Now if afterwards it be daily, warily and prudently nourished, and fed with the secret of man's bloud, and conserved for forty weeks in a perpetuall and equal heat of horse dung, it will thence become a true Infant, having members as those that are begot on women, but it will be far leasse: Then it is diligently to be brought up untill it grow a stripling, and begin to understand and be wise. And this secret is known to the Nymphs of the Wood, and the Gyants which are sprung from thence; for, there are also great and miraculous men made, who are conquerors, and skillfull in secrets, because they are borne by Art, therefore Art prevailes in them; for it is borne in them, but they are not taught of others, being called the sons of Woodmen and Nymphs, because in respect of their virtue they are not like men, but spirits.
"Campanella, though he confesseth experience had not as yet brought him to the understanding of this mystery, and therefore after some scanning of the matter doubts not of the efiect, yet he dares not deny it: for where there is something like unto the wombe, and Intelligence, if it become a humane body, God denies not to enfuse a mind: but where God reveales not, he is silent; as for Paracelsus his conceit, that Giants and Nymphs were artificially borne, that he saies is false; for the first ought to be borne without humane Art: and that they used Art to the Generation of men and not Nature seems irrationall and false, unlesse the Intelligences, the Executrices of Gods providence have used this Art in some Region; as God in the forming of Adam, which is uncertaine; besides, saies he, I think it false, that those that are gotten by Art are more prudent than those who are gotten the natural] way, and their Teachers, for Nature is wiser than Art, since Art is but her Disciple.
“Thus have we heard of the Pigmies of Paracelxux, that is his non-Adamiticall men, or middle natures, betwixt Men and Spirits; wherein he hath gone some way to meet their wish who desire to propagate the world without conjunction with women. The ground of whose Vote is supposed to be, that they had sensibly observed in impotency or totall privation of that which Eunuchs by Nature have, prolongeth life, they living longest in every kind, that exercise it not at all, Castrated Animals in any kind, as well as Spado’s by Art, living longer than they that retaine their Virilities; for, the Generation of bodies (as one, once of this Sect said) is not effected, as some conceive of Soules, that is, by Irradiation, or unanswerable to the propagation of Light, without its proper diminution, but therein a proper transmission is made materially from some parts, and Ideally from every one, and the propagation of one in a strict acception, is some minoration of the other. The Generation of one thing i: the corruption of another, although it be substantially true concerning the forme and matter, is also dispositively verified in the Efficient or Producer.”


Although this assertion of Paracelsus may be regarded merely as a case of reversion to the symbolism of the older alchemists, his directions are so detailed and the entire statement is so clear that such an explanation does not appeal to me. Indeed, from the other things that Paracelsus says about putrefaction and its relation to the generation of life, it seems more likely that he accepted such an origin of homunculi as really proved. Since the belief in spontaneous generation survived the time of Harvey, this belief on the part of Paracelsus is no discredit to him, although his statement sounds rather daring.

Harvey’s Attitude Toward Generation

Although Willis declared that Harvey wrote his treatise on generation “in the harness of Aristotle” and “with the bit of Fabricius in his teeth,” and Whitman stated that Harvey’s conception of epigenesis and of. ex 0720 on/mia was that of Aristotle, it seems to me that Harvey’s attitude regarding generation may have been quite different after all. It is possible that Aristotle experimented more than the extant records show, but according to these he seldom resorted to it_ while Harvey often did so. Harvey apparently regarded things far more from a dynamic or functional viewpoint. This is shown by his investigations on the circulation of the blood and by his many experiments on reproduction in mammals. I have not been able to ascertain what materials he used or what mammals he worked with aside from deer, but there is no doubt that he made a serious attempt experimentally to determine the permeability of the uterus and tubes to sexual products. Since the injected masses which Harvey used did not pass into the cavity of the uterus or through the tubes, in animals which he supposed were non-pregnant, he naturally concluded that these organs are impervious to sperm and ova and that the conceptus arises de novo in the uterus through a mysterious influence of the sperm, akin to the influence of the stars upon human destiny. This view was Aristotelian, to be sure.


It seems strange that Harvey, the corypheus of anatomy, as Bulwer called him, could not find the conceptus in the mammalian uterus until two months after mating, and had he had more faith in lenses he would probably have discovered the mammalian spermatozoéin and the blood capillaries as well. It is true that his refusal to believe in the existence of lacteals, rediscovered by Asselli in 1622, suggests that he was not open to conviction on all things, but who among us is. Harvey may have been unfortunate also in the animals which he examined for lacteals, and the same thing may have been true of those in which he tried to inject the uterus and the tubes. Harvey may have assumed that the animals, probably deer, were non-pregnant while they may have been pregnant and the injected material hence have been prevented from penetrating into the lumina of the uterus and tubes. He also may have made vaginal injections only.


It seems unlikely to me that Harvey espoused the theory of epigenesis solely upon the basis of embryological experiments and investigation. It is more probable that he adopted it also because of his general attitude toward things biological, which was functional, as stated. To Harvey, as to Aristotle and Heraclitus, things were becoming and never at rest as they were to Permenides and Plato and to others long after that. Even that “abyss of learning,” the great Haller, thought that there was no such thing as becoming.


It remains a puzzle why Harvey, to whose observations and experiments on the circulation of the blood the world owes so much, held so many strange ideas regarding generation. Cole suggests that he collected these ideas in the course of many years and did not revise the notes at the time when he seems to have been persuaded by Ent to publish them, and it is certain that if Harvey had resorted more to experiment in connection with generation, he would have found it necessary to reject many of the strange ideas that he entertained and suggested, some of which he himself characterized as fables.


The early existence of a belief in the spontaneous generation of insects and other animals need surprise no one who recalls that the nostrils and heads of living deer and sheep were long known to be infested with larvae and that ants, fish, birds, and so forth were infested both with internal and with external parasites. Mites of various kinds were generally supposed to arise in body filth as animalcules did in putrefying matter. Reference has already been made to the many experiments that Redi did with caterpillars, insects, and putrefying animal and vegetable matter to decide this question, and one cannot doubt him when he says at the beginning of the above mentioned letter:

“Thus, having recently made many experiments especially in regard to the origin of those living creatures considered, to the present day, by all schools to have been generated by chance, that is spontaneously without parental seed, and being distrustful of myself it occurred to me that I might have recourse to you, Signor Carlo, as you have graciously given me a place among your closest friends.”


Fig. 2. — Buffon’s microscope. (8.) The Best lens, (b) Cuffs lens No. 4, (c) an English lens No. 0. The latter was used by Ledermuller and he says that it magnified eighty six times as high as Buffon's lenses.

Views Of Redi

One cannot read Redi without feeling the highest admiration for him because of his attitude and modesty and his appreciation of his predecessors, such as Harvey. He recorded his experiments in such detail and with such candor that no one need be in doubt regarding his results and he even suggested the repetition of them by others. Redi showed the same candor when speaking of some of the apocryphal things recorded by Father Kircher, although he exclaimed, regarding the latter’s conception that dead flies give rise to living ones, “But, oh, how this single experiment must have delighted and elated those persons who fondly imagined that they could recreate man from man’s dead body by means of fermentation, or other similar or still more extraordinary processes !” Redi refers to the “folly of the charlatan, Paracelsus, who, impiously, would have us believe that there is a way to create mannikins in the retorts of alchemists.” He also refers to “Sir Kenelm Digby, who tried to prove the same by recreating crabs out of their own salts by chemical means.” Paracelsus, to whom we owe much for his emphasis on chemicals and their use in medicine, very clearly was over impressed by the accomplishments of the chemists; but he is not alone in this, for a chemist recently- predicted that the chemistry of the cell would be simple and a contemporary physiologist declared that physiologists know quite well what life is!


By a series of careful experiments Redi proved that worms (larvae) do not arise out of the “dung” but from the eggs of flies, and he showed that this holds for many other insects as well. When considering the old belief that bees arise from the putrefying carcasses of bulls, he referred to Virgil’s lines in which the latter declared that burial of the carcass was not a necessary condition, and then described his own experiments proving that insects do not arise from putrefaction, making many very interesting references -to the older literature.


(To Be Continued)


Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Meyer AW. 1932 - Essays on the History of Embryology: Part I | Part II | Part III | Part IV | Part V | Part VI | Part VII | Part VIII | Part IX | Part X | Part XI | Arthur Meyer | Historic Embryology Papers


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